Catalytic Dehydrogenative Borylation of Terminal Alkynes by a SiNN Pincer Complex of Iridium

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Abstract

Compounds with carbon-boron bonds are versatile intermediates for building more complex molecules via the elaboration of the carbon-boron bonds into other carbon-element bonds. The synthesis of carbon-boron bonds by catalytic dehydrogenative borylation of carbon-hydrogen bonds with dialkoxyboranes (RO)2BH is particularly attractive. It has been demonstrated for a variety of carbon-hydrogen bond types but not for the C(sp)-H bonds of terminal alkynes, for which hydroboration of the triple bond is a competing process. We report a new iridium catalyst that is strictly chemoselective for C-H borylation of terminal alkynes. The key to the success of this catalyst appears to be the new ancillary SiNN pincer ligand that combines amido, quinoline, and silyl donors and gives rise to structurally unusual Ir complexes. A variety of terminal alkynes (RC≡C-H) can be converted to their alkynylboronates (RC≡C-Bpin, where pin = pinacolate) in high yield and purity within minutes at ambient temperature.

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